The Vought F5U: Missed it by that much...

Once upon a time, NACA engineer Charles Zimmerman postulated that a very low-aspect-ratio wing would provide low-speed lift and short takeoff and landing performance. The wing ultimately became a disc with large propellers mounted at the forward outboard edges and rotating in opposite directions to the wingtip vortices. These made the wing even more effective at low speeds and increased the effective aspect ratio for cruise. Wind tunnel testing established the feasibility of the concept. Zimmerman joined Vought in 1937 where he designed and flew a model that demonstrated the configuration's potential for very low speed flight. Vought proposed a concept demonstrator, its V-173, to the Navy, which was intrigued enough to provide Vought with a contract for one in May 1940.

The V-173 was not small but fortunately it was light, a wooden and metal frame covered by fabric, since it was only powered by two 80-hp Continental engines.

Its first flight was on 23 November 1942. It was almost its last, since Boone Guyton found it difficult to get it turned back around to return for landing. Control modifications were made before its next flight that provided better handling qualities.

The Navy had already ordered a production version, the F5U. It was exactly the same size as the V-173, but of all-metal construction and powered by two 1,350-hp P&W R-2000 engines.

The mockup had three-bladed propellers but it was soon apparent to the engineers that the installed power and necessary rotor-hub gimbal (the blades had to "flap" to relieve root bending loads) dictated a design with four blades.

The development of the propellers and qualification of the gearboxes that interconnected the engines and the propellers delayed the program. It may have made its first low-power ground runs with F4U propellers. (The left-hand one appears to have the propeller blades rotated 180 degrees in the hub.)

The F5U's propellers had a much larger root chord and the opposed blades were paired. Note that the blade pairs were also staggered fore and aft.

The F5U was finally ready to fly in March 1947 but by then it was apparent that new fighters would be jet propelled. Although the F5U reportedly made short hops down the runway at Sikorsky Field, a first flight was not accomplished before the Navy terminated the program and directed that the prototype be destroyed.

Fortunately for aviation enthusiasts, Vought donated the V-173 to the Smithsonian. It languished at the Silver Hill storage facility for many years before being shipped to Grand Prairie, Texas where Vought Heritage volunteers restored it to like-new condition. It is now on display at the Frontiers of Flight Museum in Dallas, Texas. See http://www.flightmuseum.com/